During annual on my C-172H the mechanic (in another state) overfilled the gas in the nose wheel strut. Now I have about 5" of strut extension when 3 - 3 1/2" is apparently the right amount. As a result, the nose is high and the plane wants to take off before rotation speed is reached (angle of attack is artificially high). It also appears to shimmy somewhat more on take-off and landing roll and steering feels a bit restricted though this could be my imagination. Not wanting to fly back to the mechanic who did the annual, my question is how can I release the pressure myself in the strut...i.e. how do I access the valve at the top of the strut (seems hard to access) and what kind of tools are needed to remove the cap and release some pressure? How do I keep from over-releasing nitrogen and swinging the pendulum to the opposite direction? Thanks very much, Steve
Thanks Magman. Are there any tricks to accessing the valve at the top of the strut to relieve some gas? (e.g. any special tools required?) I'm new at this. Thanks much, Steve
Should be a shrader valve that looks similiar to the valve on your car. Simply remove the cap (usually yellow) and slowly turn the nut at the bottom of the valve...I think it is a 11/16th wrench. Normally there will be a initial loosening of the valve and will become eaisily turned by hand, and will then again become tighter (this is where you will need to be careful, since you dont have any more nitrogen to refill). Slowly turn the valve with the wrench again until you hear a small amount of air escaping, then close the valve, pull down on the prop a couple of times to get the nose to drop, then if more is needed repeat the above steps until you get the desired dimension. If you end up letting out too much air you will need to get the strut reserviced with nitrogen.....some places might not even charge you to do this.
Cessna Tech Wrote:
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> Should be a shrader valve that looks similiar to
> the valve on your car. Simply remove the cap
> (usually yellow) and slowly turn the nut at the
> bottom of the valve...I think it is a 11/16th
> wrench. Normally there will be a initial
> loosening of the valve and will become eaisily
> turned by hand, and will then again become tighter
> (this is where you will need to be careful, since
> you dont have any more nitrogen to refill).
> Slowly turn the valve with the wrench again until
> you hear a small amount of air escaping, then
> close the valve, pull down on the prop a couple of
> times to get the nose to drop, then if more is
> needed repeat the above steps until you get the
> desired dimension. If you end up letting out too
> much air you will need to get the strut reserviced
> with nitrogen.....some places might not even
> charge you to do this.
The valve that is referenced above is used in High Pressure situations. These valves are rarely used in Cessna Nose Struts. BEFORE you use a wrench to "loosen" the valve, be sure you know what you have. In servicing a high pressure shrader valve the the above procedure is correct, however, loosening a low pressure shrader valve to bleed off pressure will get you hurt. The type of valve most likely installed in your configuration is similiar to a tire valve, as referenced above, and simply depressing the valve core quickly will bleed off excess pressure, good luck and be careful....
Thanks very much for the helpful information. I did let out a bit of air from the schrader valve (2X) and rocked the nose to make sure it set. You were right in saying it would be extremely easy to release too much pressure! I almost did but avoided the pendulum swing and the strut now seems to be set right. Thanks again for all your help. Steve
